Pole wheels may be used as speed sensors or angle sensors. One typical field of application is electric drives for vehicles. Thus, pole wheels are used in angle and commutation sensors to generate signals as a function of the rotational motion of a component. Pole wheels are frequently used, for example, as signal encoders for ABS and speed sensors. Pole wheels include a disk-shaped or annular carrier, which has at least one path of magnetic north and south poles. The magnet poles are used as an etalon and may be sampled contactlessly with the aid of magnetic field sensors.
WO 2012/038169 A1 shows a sensor system for measuring the rotational speed of a rotatable machine element, in particular a wheel hub, including a signal encoder and a first and a second sensor. The signal encoder is coupled to the rotatable machine element and is situated concentrically with respect to its rotation axis and has information areas of two different types which alternate in the circumferential direction. The first sensor interacts with one information area and the second sensor interacts with a boundary area between two adjacent information areas. An information area of the first type is preferably designed as a magnetic plus pole, and an information area of the second type is designed as a magnetic minus pole.
An angle measuring device for a crankshaft of an internal combustion engine is known from DE 10 2004 010 948 B4. The angle measuring device includes a supporting body having a first magnetic path designed as a circular ring area and a second path designed as a cylindrical lateral area. Each path may be sampled by at least one electromagnetic sensor.
DE 102 10 372 A1 describes a rotation angle sensor, which includes a disk-shaped carrier of a first path of magnetic north and south poles and a second path of magnetic north and south poles with a number of north and south poles which deviate from the first path, and each including a sensor element for detecting the first and second paths. After startup of the rotation angle sensor, a first rough detection of the rotation angle of the path carrier is carried out with the aid of the first path, and a high resolution detection of the rotation angle is implemented with the aid of the second path. The sinusoidal signal of the rotation angle sensor is linearized by applying an angle function.
The pole wheels used in the prior art naturally have nonlinear characteristics of their field profiles with respect to the pole wheel position. If only the angular position of the pole wheel needs to be detected with an accuracy which corresponds approximately to the distance between adjacent poles, the pulses generated by the poles at the sensor may be evaluated. In particular, if the position between two adjacent poles is to be determined more precisely, the evaluation of the nonlinear characteristics presents considerable difficulties. To obtain a desired magnitude of linear signal characteristic in many applications, it is known to subsequently linearize the signal detected by the sensor on a microcontroller or in a control unit with the aid of suitable software algorithms. A problematic aspect of this procedure is that the computational linearization of a sensor signal generally covers a sensitivity which is unevenly distributed over the measuring range. A signal which is already originally linear is much more robust and responds to tolerance fluctuations in the same manner over the entire measuring range. It is furthermore disadvantageous that the microcontroller and the software algorithms used for the linearization incur costs. The nonlinearity of the signal must also be known in order to be able to apply a suitable linearization algorithm thereto.
It is furthermore known to use pole wheels which are specifically adapted to the particular application. However, this has the great disadvantage that special pole wheels are much more expensive to manufacture than are more basic components. In addition, standard ABS encoders, in particular, are so widespread that they may be mass produced and may thus be very easily acquired.